The present invention relates generally to Molecular Bearn Epitaxy (MBE) and more specifically to a method of growing homoepitaxial silicon carbide (SiC) using MBE.
The physical and electronic properties of SIC make it a desirable candidate semiconductor material for many applications. Because of its large thermal conductivity, breakdown voltage, and electron saturation velocity, SiC is ideal for the fabrication of devices such as high frequency power devices, solid state phased array radar systems and high frequency power supplies, as well as high power devices such as power electronics for power generating systems and surge suppressors, for example. Since the bandgap of SiC is large (3.03 eV for 6H-SiC), it is also well suited to high temperature and optoelectronic applications. Moreover, SiC exists in a wide variety of stable polytype forms and, therefore, has the potential for use in novel devices utilizing heterostructures of different polytypes. Advantageously, such devices would be nearly stain-free, due to the low basal plane lattice mismatch between polytypes (Δa/a≈0.0005 for 3C/6H). Lastly, there would also be little or no contribution to heterostructure interface energy due to chemical potential differences.
While the usefulness of SiC is well known, the present methods of fabrication generally give less than satisfactory results. For example, the current practice of growing SiC for most commercial applications involves the use of a chemical vapor deposition technique. While somewhat successful, the SiC grown by this technique is expensive and lacks sufficient quality and purity for widespread use in electronic applications.
In order to overcome these limitations, recent efforts to grow the desired high purity layers of SiC have incorporated the MBE method. MBE is well known to those skilled in the art. Generally, according to the MBE method, the constituent elements of the desired semiconductor material are placed into the MBE chamber and converted into molecular beams by one of several methods, such as direct heating, electron beam impringement, and the like. The beams thus generated are directed onto a heated substrate within a growth chamber. The desired layers of material are grown upon the substrate by flux deposition over a period of time. MBE can provide extremely high purity results when the source materials and substrate are highly purified and the process ensues in an ultra high vacuum environment. The MBE method provides a high degree of control over the growth process, and as a result is well suited for the production of high quality semiconductor materials.
Thus, while the solution to the purity problem would appear to lie in the use of MBE to grow SiC, it is known that a problem lies in the inability of SiC to be reliably grown using MBE, especially homoepitaxial SiC wherein SiC layers are grown upon a SiC substrate. One recent SiC MBE technique has demonstrated heteroepitaxial growth of 3C-SiC films on Si using C60 and Si effusion cells, and the films exhibit a lower stacking fault density and show no evidence of twinning or mixed polytypes. This technique, while somewhat successful utilizes the sublimation mode of beam generation and, accordingly, provides less than desirable results.
Another recent SiC investigation utilizing the MBE technique, has resulted in the growth of 6H-SiC epitaxial layers on Si (111) and 6H-SiC(0001) by solid-source MBE using silicon and carbon flux generated by electron-beam sources. While somewhat successful, this technique also gives less than desirable results because the flux generated by the electron-beam is unstable and results in inconsistent material growth; not a solution to the problem of poviding high quality SiC semiconductor material, and especially homoepitaxial SiC.
A need exists therefore for a method of reliably growing homoepitaxial SiC utilizing the desirable MBE method and providing high quality, high purity SiC deposition.